Interpretive Summary: Urban residents often do not practice tick control by applications of synthetically produced acaricides because of potential hazards and adverse environmental impacts related to the general toxicity of most of those available. We developed encapsulated formulations of nootkatone, a relatively non-toxic (to people and animals) component of essential oil from grapefruit to prevent phytotoxic damage to treated plants and extend the residual activity by slowing volatility of nootkatone. The encapsulated formulation improves the potential for commercialization of nootkatone as a natural pest control product. Ultimately, the public will benefit from the successful development of a natural pest control product that kills disease vectoring ticks with no adverse environmental impacts.

Technical Abstract:
Nootkatone is a component of grapefruit oil that is toxic to the disease vectoring tick, Ixodes scapularis Say, but unfortunately causes phytotoxicity to treated plants and has a short residual activity due to volatility. We prepared an encapsulated formulation of nootkatone using lignin to compare with a previously used emulsifiable formulation for nootkatone volatility, plant phytotoxicity, and toxicity to unfed nymphs of I. scapularis. Volatility of nootkatone was measured directly by trapping nootkatone vapor in a closed system, and indirectly by measuring nootkatone residue on filter paper after exposure to simulated sunlight (Xenon). After 24 hours in the closed system, traps collected only 15% of the nootkatone applied as the encapsulated formulation compared with 40% applied as the emulsifiable formulation. After a 1-hour light-exposure, the encapsulated formulation retained 92% of the nootkatone concentration on the filter paper compared with only 26% retained by the emulsifiable formulation. For plant phytotoxicity, cabbage leaves treated with the encapsulated formulation expressed less necrosis, retaining greater leaf weight when compared with leaves treated with the emusifiable formulation. The nootkatone in the emulsifiable formulation was absorbed by cabbage and oat plants (41 to 60% recovered 2 hours after application, respectively), as opposed to 100% recovery from the plants treated with encapsulated nootkatone. Using a treated vial technique, toxicity of encapsulated nootkatone (LC(50) = 9 ng/cm(2)) was not significantly different from toxicity of the emulsifiable formulation (LC(50) = 17 ng/cm(2)). Thus, the encapsulation of nootkatone maintained toxicity for tick control, reduced nootkatone volatility and reduced plant phytotoxicity.